GB-A-1 465 973 ( whose United States equivalent is U.S. Pat. No. 3,871,947), describes a coextruded two-layer polyester film, of which one layer consists of isophthalic acid-and terephthalic acid-containing copolyesters and the other layer consists of polyethylene terephthalate. There is no useful information about the sealing behavior of the film in the document. Owing to lack of pigmentation, the film is not windable and not further processible.
EP-A-0 035 835 describes a coextruded sealable polyester film to which particles whose mean particle size exceeds the layer thickness of the sealing layer are added to improve the winding and processing performance in the sealing layer. The particulate additives form surface projections which prevent the undesired blocking and adhesion of the film to rollers or guides. It remains unclear whether the other, nonsealable layer of the film comprises antiblocking agents. The seal seam strength is measured at 140° C. and is within a range from 63 to 120 N/m (corresponding to 0.97 to 1.8 N/15 mm of film width).
EP-A-0 515 096 describes a coextruded multilayer sealable polyester film which comprises an additional additive on the sealable layer. The additive may comprise, for example, inorganic particles and is preferably applied as an aqueous layer to the film in the course of production thereof. This is intended to maintain the good sealing properties and ensure that the film has good processability. The reverse of the film contains only very few particles, which get into this layer principally via the regrind. There is no information in this document regarding the sealing temperature range of the film. The seal seam strength is measured at 140° C. and is more than 200 N/m (corresponding to 3 N/15 mm of film width). For a sealing layer of thickness 3 μm, a seal seam strength of 275 N/m (corresponding to 4.125 N/15 mm of film width) is reported.
EP-A-1 138 480, ( whose United States equivalent is U.S. Pat. No. 6,423,401B2), describes a biaxially oriented sealable polyester film with a base layer B, a sealable top layer A and a further, nonsealable top layer C. The sealable top layer A has a minimum sealing temperature of not more than 110° C. and a seal seam strength of at least 1.3 N/15 mm of film width. The topographies of the two top layers A and C are characterized by particular features. The inventive film is suitable particularly for use in flexible packages, and especially for use on high-speed packaging machines. This film can achieve only very low adhesion to PVC.